Hydrogen containers or storage canisters are widely used in for example hydrogen powered vehicles, hydrogen fuel cell systems and related products thereof, and hydrogen generation systems for storage of hydrogen. Currently, mass storage of hydrogen takes three forms including liquid form, high-pressure gas form and low-pressure metal hydrides. Among the three forms the solid metal hydride is the best option in respect of operation safety.
Metal alloys used to store hydrogen in room temperature and low-pressure conditions include TiFe alloy, LaNi5 alloy, and Mg alloy (all of which are in powder form.) These powders are contained in a storage canister for ease of usage and carrying. The storage canister must be properly charged with hydrogen gas before usage and a discharge process must be carried out to release hydrogen from the storage canister to supply for example a hydrogen engine or a hydrogen fuel cell.
In practical operation of the hydrogen storage canister, the available remaining amount of hydrogen remaining in the hydrogen storage canister must be constantly monitored in order to timely recharge the hydrogen storage canister with hydrogen. For example, for a portable fuel cell power generator that obtains hydrogen supply from a hydrogen storage canister, or for an electrical motorcycle/bicycle powered by hydrogen, a user must keep aware of the remaining amount of hydrogen inside the hydrogen storage canister in order to determine the time period within which the device is still operable with proper supply of hydrogen or to determine the time to recharge the hydrogen storage canister with hydrogen or to replace the hydrogen storage canister with a new or a fully charged one.
The performance of a solid alloy powder hydrogen storage is often indicated by a PCT curved that involves the parameters including operation pressure, operation temperature and hydrogen capacity. FIG. 1 of the attached drawings shows PCT curves of TiFe alloy for the storage of hydrogen in different temperatures, while FIG. 2 shows similar curves for LaNi5 alloy in different temperatures. In these drawings, abscissa indicates the hydrogen capacity, and ordinate indicates the relief pressure (atm) of hydrogen gas.
It is clear from the curves of FIGS. 1 and 2 that except for extremely high and low pressures zones the characteristic curves of hydrogen are quite flat with respect to the capacity. In other words, measuring pressure change cannot properly tell the capacity change of a hydrogen storage canister. Further, although the curves of hydrogen capacity are sensitive to temperature, their change with respect to temperature is substantially regular. However, since the hydrogen capacity is also subject to change of pressure, there is no way to determine the hydrogen capacity by simply measuring temperature.
It is very common in laboratories that to determine the hydrogen capacity of a hydrogen storage canister by measuring weight difference; this needs precision instrument to perform precise measurement of the weight of the hydrogen container and calculate the difference between successive measurements to estimate an approximation of available hydrogen capacity for the particular hydrogen container. However, in practical applications, besides the hydrogen container itself, a hydrogen storage/supply system also includes a plurality of related parts/members/components, such as heat exchanger water jacket, fast connector, and cooling water, and variation of overall system weight is great between different systems. Furthermore, installation of weighing devices complicates the construction of whole system. All these factors make it very difficult to estimate hydrogen capacity by weight measuring in most of the practical applications.
In addition, actual hydrogen capacity of solid metal alloy hydrogen storage varies with the purity of hydrogen stored and the poisoning of alloy. Besides, the hydrogen capacity reduces with the operation cycles of charging/discharging of hydrogen. Moreover, what is actually needed is the available remaining hydrogen capacity of a hydrogen storage canister, rather than the overall hydrogen capacity of hydrogen storage canister. The actual available remaining hydrogen capacity is related to the temperature of the hydrogen storage canister, actual hydrogen pressure used, and the flow rate of hydrogen.
Heretofore, no efficient and precise method or device is available for commercial use in measuring the hydrogen capacity of a hydrogen storage canister. This delays the promotion of use of hydrogen in different applications including fuel cells and fuel cell powered electrical vehicles.
Thus, the present invention is aimed to overcome the above-discussed difficulty and to provide a useful method for practically determining the hydrogen storage.